package com.yangluyao.test.自旋;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @author YLY
 * @ClassName ReentrantReadWriteLockDemo
 * @Date 2020/5/6
 * @Version 1.0.2
 * 多个线程同时读一个资源类没有任何问题，所以为了满足并发量，读取共享资源应该可以同时进行
 * 但是
 * 如果有一个线程想去写共享资源，就不应该再有其他线程可以对该资源进行读或者写
 * 小总结：
 * 读---读  能共存
 * 读---写 不能共存
 * 写---写 不能共存
 *    写操作：原子+独占，整个过程必须是一个完整的统一体，中间不许被分割，被打断
 */
public class ReentrantReadWriteLockDemo {
    public static void main(String[] args) {
        MyCache myCache = new MyCache();
        for (int i = 1; i < 5; i++) {
            final int timeInt = i;
            new Thread(() -> {
                myCache.put(timeInt + "", timeInt + "");
            }, String.valueOf(i)).start();
        }

        try {
            TimeUnit.SECONDS.sleep(3);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        for (int i = 1; i < 5; i++) {
            final int timeInt = i;
            new Thread(() -> {
                myCache.get(timeInt + "");
            }, String.valueOf(i)).start();
        }
    }
}

class MyCache {
    private volatile Map<String, Object> map = new HashMap<>();
    private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();


    public void put(String key, Object value) {
        lock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t  正在写入：" + key);
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "\t  写入完成：");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.writeLock().unlock();
        }
    }

    public void get(String key) {
        lock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "\t  正在读取：");
            try {
                TimeUnit.MILLISECONDS.sleep(300);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Object result = map.get(key);
            System.out.println(Thread.currentThread().getName() + "\t  读取完成：" + result);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.readLock().unlock();
        }
    }
}